Perpendicular magnetic recording has been developed in part to achieve higher recording density than is realized with longitudinal recording devices. A PMR write head typically has a main pole with a small surface area at an air bearing surface (ABS), and coils that conduct a current and generate a magnetic flux in the main pole such that the magnetic flux exits through a write pole tip and enters a magnetic medium (disk) adjacent to the ABS. Magnetic flux is used to write a selected number of bits in the magnetic medium and typically returns to the main pole through two pathways including a trailing loop and a leading loop in a so-called double write shield (DWS) structure. The trailing loop comprises a trailing shield structure with a side at the ABS and a portion that extends over the write coils and connects to a top surface of the main pole layer above a back gap magnetic connection. The leading loop includes a leading shield with a side at the ABS and that is connected to a return path proximate to the ABS. The return path extends to the back gap connection and enables magnetic flux in the leading loop pathway to return from the leading shield at the ABS and through the back gap connection to the main pole layer. A PMR head which combines the features of a single pole writer and a double layered medium (magnetic disk) has a great advantage over LMR in providing higher write field, better read back signal, and potentially much higher ADC.
For both conventional (CMR) and shingle magnetic recording (SMR), continuous improvement in storage area density is required for a PMR writer. A write head that can deliver or pack higher bits per inch (BPI) and higher tracks per inch (TPI) is essential to the area density improvement. A fully wrapped around shield design also known as an all wrap around (AWA) shield structure for a PMR write head is desired where the trailing shield is responsible for improving down track field gradient while side shields and a leading shield improve the cross track field gradient and TPI as well as adjacent track erasure (ATE) performance. To avoid wide adjacent track erasure (WATE), all shields are typically made of a <19 kG material that is CoFe, NiFe, or CoFeNi. A double write shield (DWS) design may be employed wherein the main pole is comprised of high moment (>19 kG to 24 kG) material. If writeability can be sustained, a thinner write gap at the main pole trailing (top) surface and a narrower side gap adjoining the main pole sides in the cross-track direction are preferred for better track field gradient (Hy_grad, BPI) and cross-track field gradient (Hy_grad_x, TPI), respectively.
In hard disk drives (HDD), WATE is one of the most critical issues for PMR writer designs. Both micromagnetic modeling that is described by S. Song et al. in “Micromagnetic analysis of adjacent track erasure of wrapped-around shielded PMR writers”, IEEE Trans. Magn., vol. 45, no. 10, pp. 3730-3732 (2009), and experimental data described by Y. Tang et al. in “Characterization of Adjacent Track Erasure in Perpendicular Recording by a Stationary Footprint Technique”, IEEE Trans. Magn., vol. 49, no. 2, pp. 744-750 (2013) indicate that one root cause of WATE is the stray field from side shields and leading shield during the dynamic writing cycles. It is observed that adjacent track erasure has strong writing frequency dependence and can be expected to be much more severe as increased ultra-high data rate HDDs are produced in the future.
Thus, the key to an optimized PMR writer structure is the capability to control distribution of magnetic flux from the main pole to each shield. Ideally, better control of magnetic flux in the near field or proximate to the main pole is desirable to minimize WATE while maintaining ADC. Improved shield design is required for tuning magnetic flux distribution to enable PMR writers with higher TPI capability to at least 400K/in for CMR and at least 500K/in for SMR.